1. Field of the Invention
The present invention relates to a method for producing a fatty acid lower alcohol ester employing a lipase, and a microorganism containing a lipase suitable for the method.
2. Description of the Prior Art
In general, fossil fuels typified by petroleum and light oil are used as fuels for automobiles. These fossil fuels, especially, light oil used in diesel automobiles contain a large amount of nitrogen compounds and sulfur compounds, so that a large amount of gas such as CO2, NOx, and SOx are exhausted from automobiles such as diesel automobiles. Since these exhaust gases cause global warming and environmental pollution, reduction of the exhaust amount is an issue to be solved urgently.
As an alternative fuel to fossil fuels such as light oil, there are high expectations in so-called biodiesel fuel, which uses oils and fats produced by naturally occuring plants, animals, fishes or microorganisms. Among these oils and fats, the oils and fats used for food production are often dumped into the environment and cause environmental problems. Therefore, expectations in biodiesel fuel made from waste oil are particularly high in view of prevention of air pollution and effective utilization of waste oil.
Fatty acid lower alcohol esters are preferably used as biodiesel fuels. In order to produce fatty acid lower alcohol esters from oils and fats, a technique for separating an oil and fat into the glycerin and a fatty acid constituting it, and then producing an ester from an alcohol and a fatty acid is required. As one of the methods, a variety of research on the production of fatty acid esters using a lipase is conducted.
However, the method used at present is to dissolve an oil and fat in a solvent (e.g., hexane, etc.) in order to react the oil and fat using a lipase in the presence of an alcohol. In this method, it is necessary to separate fatty acid esters from the solvent, which requires an operation for collecting the solvent, and therefore the process becomes complicated and the cost increases. In addition to these disadvantages, there is the danger of explosion. For these reasons, it is attempted to develop the method in a solvent-free system.
An experimental example using a solvent-free system is described in JAOCS vol. 73, pp. 1191–1195 (1996). According to this experiment, when branched alcohols such as isopropanol, isobutanol, and 2-butanol are used, a fatty acid ester can be obtained in a ratio of 90% or more. However, when industrially used inexpensive alcohols such as methanol and ethanol are used, the fatty acid esterification reaction hardly proceeds. Thus, at present, a method for producing non-energy consumption type biodiesel (fatty acid ester) using an inexpensive alcohol in a solvent-free system has not been established yet.
On the other hand, in a synthetic reaction of a fatty acid ester using a lipase, a method using a lipase which is isolated and immobilized has been most commonly examined. However, this method has the problem of taking much time for the isolation and immobilization of the lipase.
Furthermore, it is also under examination that a microorganism itself is used. The need of considering the permeability of the cell membrane has been pointed out, so that a treatment of the microorganism with a solvent such as an alcohol is under examination (for example, see Felix et al., Anal. Biochem. 120: 211–234 (1982)). This solvent treatment also requires time and cost for the treatment and the collection of the solvent, and has the problem of the danger of explosion.
Furthermore, a transesterification using a lipase is carried out in a nonaqueous system in view of hydrolysis of a produced fatty acid ester. In particular, when waste oil containing a large amount of water is used, the progress of the reaction is inhibited. Therefore, facilities for removing water are necessary, which increases the cost. A method for producing a fatty acid lower alcohol ester in the presence of water is described in Japanese Laid-Open Patent Publication No. 64-10994. However, in this method, a special enzyme has to be used, and isolation of the enzyme takes time and costs, so that this method has not been put to practical use.
Thus, in the transesterification using a lipase, none of the above problems has been solved so that there is a demand for a method for producing a fatty acid ester more efficiently.